1. Field of the Invention
The present invention relates to an ablation apparatus for ablating a convex part on a rough surface of an object, and more particularly to the ablation apparatus suitable for correcting roughness on the surface of a cornea by ablating selectively only the convex part on the surface of the cornea having irregular astigmatism and the like.
2. Description of Related Art
Recently it is known in general that PRK (Photorefractive Keratectomy) is utilized for correcting an ametropia of an eye by ablating the surface of the cornea by a laser beam and by changing its curvature, and PTK (Phototheraputic Keratectomy) is applied for removing a diseased portion on the surface of the cornea by ablating with the laser beam. The ablation by the laser beam for performing the PRK and PTK has been carried out by the following three methods.
The first method is to ablate a predetermined area by a laser beam having large area all at once, the second method is to ablate a predetermined area by moving a rectangular laser beam, and the third method is to ablate a predetermined area by making it scan a small spot in a two-dimensional way.
However, the human cornea is not always like a spherical surface or toric surface, but the surface of the cornea happen to be roughness partially due to the irregular astigmatism and the like. When it is try to make the surface of the cornea to be a spherical surface or a toric surface by ablating with a laser beam, in the case of the first method that applies a beam having large area or the second method that moves the rectangular laser beam, since each convex part had to be ablated one by one in a manner that adjusting an irradiation area to the convex part, it results in such disadvantage that it takes much more time.
On the other hand, in the case of the third method that scans a small spot, convex parts can be ablated in less time compared with the first and the second methods, the ablation is carried out by scanning and ablating selectively only the convex part. However if there are many convex parts to be ablated, it also results in such disadvantage that it takes relatively much time.